The web’s previous highest non-sport or film audience was for the preem of Matt Le Blanc’s sitcom “Joey” in February 2005, which won an overnight rating of 4.1 million viewers.

But Channel 5’s “Big Brother” audience was less than the 5.8 million viewers who tuned in when the seventh series bowed on Channel 4 last year.

The Big Daddy of reality shows, dumped last year by Channel 4 in the face of declining popularity, also won its slot.

This was an unusual feat for Channel 5, which under new owner Richard Desmond has relied increasingly on U.S. imports, such as “CSI.”

Torchwood: Miracle Day,” the Starz BBC co-pro that airs on the pubcaster’s flagship web, BBC1, in the U.K, only managed 3.4 million viewers against “Celebrity Big Brother.”

Desmond finally secured the U.K. rights to “Big Brother” from Endemol in April following months of tortuous negotiations.

Its initial success, driven by relentless cross-promotion in Desmond’s British papers, the Daily Star and the Daily Express, will be a big relief for Desmond and Endemol, which is highly leveraged and seeking a new CEO.

The big question is whether Channel 5 can maintain the show’s momentum throughout its run.